Typically, optical disc players such as LDPs, CDPs, CD-ROM and DVD-ROM players, DVD players, and BD and 3D players, are apparatuses including operations of: loading a disc onto a turntable by a loading mechanism; clamping, fitting and fixing a mounting hole formed at the center of the disc with a chuck that is a clamping unit; rotating the disc clamped in the chuck in one direction by a drive source of a spindle motor drive unit; and reproducing information recorded on the disc by an optical pickup unit that moves in a radial direction of the disc.
In general, the spindle motor maintains a constant contact section between the bearing and the rotating shaft, to thereby rotatably support the rotating shaft and to thus maintain high accuracy rotational characteristics, with a result of being widely employed as a hard disc drive (HDD), optical disc drive (ODD) and a driving unit for driving other recording media requiring high-speed rotation.
The spindle motor requiring high-speed rotation becomes thinner and lighter to meet development of ever-smaller electronic devices, and an example of the spindle motor is schematically shown in FIG. 1 (see Korean Laid-open Patent Publication No. 10-2010-0043525).
FIG. 1 is a cross-sectional view of a conventional spindle motor. As shown, the conventional spindle motor is combined by inserting an outer circumferential surface of the lower end of a bearing housing 13 into a coupling hole formed in a base plate 11 to thus spinning or caulking an outer protrusion 13a. Stoppers 14 and a cap 15 are coupled on an inner circumferential surface of the lower end of the bearing housing 13, in order to prevent a rotating shaft 19 from seceding, in which the cap 15 is combined by spinning or caulking an inner protrusion 13b of the lower end of the bearing housing 13.
A bearing 17 is fixed in the bearing housing 13 and the rotating shaft 19 is supported by the bearing 17, in which the rotating shaft 19 is rotatably supported by the bearing 17. A support washer 16 that is provided in the lower end of the rotating shaft 19 to reduce a rotational resistance of the rotating shaft 19 is disposed in the cap 15.
In addition, a stator 21 having a core 21a and a coil 21b is fixed on the outer circumferential surface of the bearing housing 11, and a rotor 23 having a rotor yoke 23a and a magnet 23b is fixed on the leading end of the rotating shaft 19.
The upper surface of the rotor yoke 23a of the rotor 23 plays a role of a turntable on which a disc D storing data is secured and seated. To this end, a rubber ring 12 is arranged on the outside of the upper surface of the rotor yoke 23a to thus prevent the disc D from slitting, and a chucking device 18 having a disc chuck 18b and a chuck case 18a is provided on the inside of the upper surface of the rotor yoke 23a to thus secure the loaded disc D.
The conventional spindle motor generates a rotating magnetic field when an electric current is supplied to the coil 21b, and thus the magnet 23b, that is, the rotor 23 rotates by an electromagnetic force 23b that is formed between the coil 21b and the magnet 23b, to thus enable the disc D mounted on the rotor yoke 23a to rotate.
In the case of the conventional spindle motor, since the coupling between the bearing housing 13 and the base plate 11 and the coupling between the bearing housing 13 and the cap 15 are accomplished by a spinning or caulking process of the outer and inner protrusions 13a and 13b, an assembly process becomes complicated.
In addition, when a spinning or caulking process is executed in order to perform a bonding process between the bearing housing 13 and each of the base plate 11 and the cap 15, in the conventional art, a mismatch of the verticality of the bearing housing 13 with respect to the base plate 11 will occur. As a result, when the bearing 17 is press-fitted into the bearing housing 13, a run-out problem from the verticality of the bearing 17 may occur to accordingly require a repair the run-out problem. In this case, if the rotating shaft 19 is assembled with the bearing 17 without repairing, the rotating shaft 19 is tilted from the base plate 11, and thus vibration and noise may occur.
Moreover, when the bearing 17 is press-fitted into the bearing housing 13, an inner diameter portion of the bearing 17 may change by the press-fitting force. As a result, in order to correct the change in the inner diameter portion of the bearing 17, machining of the inner diameter portion of the bearing 17 is required by a sizing process.
In addition, when a spinning or caulking process of joining the cap 15 to the bearing housing 13 is poor, oil of the bearing 17 may leak through a contact portion between the bearing housing 13 and the cap 15.
Moreover, in the conventional spindle motor, the bearing housing 13 is machined or manufactured by an extrusion process, in a CNC (Computer Numerical Control) machine by using a brass or aluminum material, to thus cause disadvantages of increasing a manufacturing cost.
Typically, various kinds of electronic devices are wounded to prevent damage to the devices due to electric shocks such as the external lightning or static electricity. In addition, the spindle motors and the disc drive devices using the spindle motors are grounded, and the spindle motors are configured to discharge electric charges due to static electricity to the outside by mounting a base plate in a disc drive unit and simultaneously through a main body of the disc drive unit.
In other words, as shown in FIG. 1, the conventional spindle motor is configured so that the base plate 11 made of metal is in mutual contact with the rotating shaft 19 through the bearing housing 13 and the bearing 17, to thus form an electrostatic discharge path.
The slim spindle motor is mounted in a notebook or laptop computer. In this case, when a disc is loaded or unloaded from the notebook or laptop computer, the spindle motor is exposed to the outside together with a tray.
As described above, when the spindle motor is exposed to the outside and then a user loads a disc on a turntable, the rotating shaft of the spindle motor acts as a lightning rod. In addition, even if the electric charges due to the electrostatic discharge (ESD) are introduced into the spindle motor through the rotating shaft, the electric charges are discharged into the main body of the disc drive unit through the electrostatic discharge path and discharged to the ground. As a result, the conventional spindle motor did not cause a problem that a drive IC (Integrated Circuit) of the motor drive circuit was damaged due to the electrostatic discharge (ESD).
Meanwhile, in the case of a DVD (Digital Versatile Disc) of a half height drive for recording the DVD, it is a current trend that a disc recording speed increases to have a recording speed of 16-times to 20-times or higher. To improve such a recording speed, the maximum rotational speed of the spindle motor should be secured to be 10,500 RPM or higher. In the case that the rotational speed of the spindle motor is enhanced as described above, the verticality of the rotating shaft becomes even more important.
To solve the problem of the conventional spindle motor, the spindle motor was proposed in Korean Patent Application No. 10-2010-0111374 on Nov. 10, 2010 by the same applicant as that of this invention, in which a bearing housing 33 is formed by using a resin and simultaneously a base plate 31 is integrated with the bearing housing 33 by means of an insert-molding, hot-melting, or bonding process, to thereby secure verticality of both a bearing 37 that is assembled with the bearing housing 33 and a rotating shaft 39, and to thereby also essentially block the leakage of oil from the bearing 37, and to thus have the advantage of simplifying an assembly process (FIG. 2).
However, in the case that the slim spindle motor that is illustrated in FIG. 2 is mounted in the notebook or laptop computer, the spindle motor may be exposed to the outside together with a tray, when a disc is loaded or unloaded from the notebook or laptop computer.
As described above, when the spindle motor is exposed to the outside and then a user loads a disc on a turntable, the rotating shaft 39 of the spindle motor acts as a lightning rod as shown in FIG. 2, and the electric charges due to the electrostatic discharge (ESD) may be introduced into the spindle motor through the rotating shaft 39. In this case, the electric charges introduced into the rotating shaft 39 can be transferred through metal components such as a bearing 37 and a rotor case 43a made of metal and being contact with the rotating shaft 39. However, since the bearing 37 is wrapped by the bearing housing 33 made of a resin and thus does not secure an electrostatic discharge path, the electric charges move to a magnet 43 along the rotor case 43a made of a magnetic path forming material (i.e., metal).
In this case, the electric charges do not proceed further in the magnet 43 and then are sufficiently collected in the magnet 43, so as to be beyond a charging capacity of a conductor. As a result, an electric charge jumping phenomenon occurs in which the electric charges are temporarily jumped to a coil 41a wound on an adjacent core 41b. 
As a result, the electric charges jumped onto the coil 41a of a stator 41 may inflict a damage on a disc drive IC of the motor drive circuit. The damaged drive IC may cause a malfunction of the spindle motor or a stop of the driving of the motor, which obstructs an optical disc player device from playing a normal role.